Production of oxalic acid.



UNITED STATES PATENT oEEioE.

FRANK AUSTIN LIDBURY, OF NIAGARA FALLS, YORK.

V ?RODUCTION OF OXALIC ACID.

No Drawing.

To all it may concern:

Be it known that I, FRANK AUSTIN Lu BURY, a citizen of Great Britain, and a resident of Niagara Falls, Niagara county, New York, (whose post-office address is 33 Sugar v street, Niagara Falls, New York), have in.-

vented a new and useful Improvement in the Production of OxalicAcid, which invention 1 C The invention consists broadly of the gen -\eration of oxalic acid by the treatment of {eeertain salts thereof with hydrochloric acid, under suitable conditions, followed by the subsequent recovery of the resultantoxalic acid.

Heretofore, in the manufacture of oxalic acid (H C O,), a first step consists of pro ducing (as an intermediate body) sodium oxalate-or potassium oxalate, or various nnxtures of the two, by the reaction of sodium (or potassium) hydrate upon various materials (such, for'instance, assawdust or the like) followed, as a second step, by the conerS O Of'tlm Oxalate or oxalates into calcium oxalate (a-second intermediate product), by boiling with lime; then, as the third step, the calcium oxalate is converted into oxalic acid, by heating with sulfuric acid; finally. as the fourth step, the oxalic acid has to be recovered from the mother liquor by evaporation and crystallization. This rocess has numerous disadvantages, among which are the following: sulfuric acid and lime are required, the whole of these two materials is decomposed and used up, so that fresh supplies are constantly needed; these two ingredients go to make up calcium sulfate, a worthless waste-product that has to be disposed of (which, in commercial operation, involves considerable expenditure); after the production of the oxalate, there are two successive chemical treatments necessary; and the evaporation of the mother liquor (containing as it does some calclum fate), to recover the oxalic acid, 15 not. easy to carry out. V My invention dispenses with the sulfur c acid and the lime; it requires only one chemr cal treatment after the production of the Specification of Letters Patent. Application filed November 22, 1911.

.ence of Patented July2, 1912.

Serial No. 661,692.

intermediate oxalate; it' does not require evaporation; and it produces no waste-i product.

My invention is based upon the fact that the reaction of hywlrocldoric acid upon 'cer-' tain salts of oxalic acid (to wit: the sodium salts) gives oxalic acid and thechlorid;-and that such chlorid is practically insoluble in strong hydrochloric-acid so.utions, while the 'oxalic acid goes into soluti0n;and (in thepreferred form of my invention) upon the further fact that on reducing the temperature of such solutions having substantial amounts of oxalic acid dissolved therein, a considerable portion of the latter body is precipitated. I take advantage of these facts by reacting upon a sodium salt of oxalic acid with hydrochloric "acid,'rinuthe presence of water and heat, and thereby produce on the one hand oxalic acid which remains in solution, and on the other hand the solid sodium chlorid which can be separated readily from the mother liquor containing the oxalic acid, and then, on lowering the temperature of the mother .liquor, oxalic acid is precipitated and recovered in solid form. My invention, however, is not limited to the use of heat and subsequent cooling, because the solid oxalic acid can be recovered from the mother liquor by other means, such as evaporation and subsequentcrystallization. My invention, then, consists broadly of treating a salt or salts of oxalic acid, particularly the sodium salts (sodium oxalate and sodium hydrogen oxalate), with hydrochloric acid in such manner as to generate sodium chlorid in solid form and oxalic acid in solution, and in then recovering the oxalic acid by any suitable means.

My invention consists further in the various steps and procedures hereinafter set forth and claimed.

The reaction of hydrochloric acid ('HCl) upon sodium oxalate (Na C O in the'preswater (H O), to produce sodium chlorid (NaCl) and oxalic acid (H,C,O,), may he expressed by the following equation:

centrated aqueous solution of hydrochloric acid, especially at normal temperature, there are ordinarily formed certain practieallv insoluble bodies and certain bodies in solution, namely, (as solids) sodium chlorid and sodiuui hydrogen oxalate, and (in solution) 5 oxalic acid with small quantities of soluble sodiumsalts. I have found, however, that this sodium hydrogen oxalate (NaHC oJ may be itself converted, by similar treatment witlrhydrochloric acid, into (solid) 'sodium chlorid and (soluble) oxalic acid, as expressed by the formula:

the latter be taken as a raw material or as an intermediate product from the reaction upon sodium oxalate), both bodies being converted into the insoluble sodium chlorid and the soluble oxalic acid. So that,'as a general proposition, the greater the amount of the hydrochloric acid, solution used per unit of the oxalate, and the greater .the'

strength of the acid solution (especially when maintained to the conclusion of the operation, by passing in hydrochloric acid gas), the more complete the reaction in producing sodium chlorid and oxalic acid, and the greater the yield of oxalic acid, and the smaller the amount of sodium salts that 40 goes into solution. In other words, by employing a relatively large quantity of the acid solution, and maintaining the concentration thereof (as by passing in the gas), the more perfectly is my invention realized; nevertheless, my invention is carried out, but not so effectively, with relatively smaller amounts of the acid solution, and with weaker solutions.

As a specific instance or formula, I take one part by weight of sodium oxalate, and put it into a solution consisting of about four parts by weight of water saturated with hydrochloric acid gas (and kept practically saturated throughout the treatment),

at a temperature of, say, about 70 centigrade, and allow the reaction to continue until the sodium oxalate has been completely disposed of, this being hastened by agitation. Sodium chlorid is thereby produced in solid form'andis removed, as by decanting off the yet-unoooled mother liq uor, and any oxalic acid adhering to the chlorid may be removed by washing the latter (preferably with concentrated hydrochloric acid solution). If the mother liquor has been kept )ractically saturated with hydrochloric acic gas, it will now contain, in solution. 1'00 grams or more per liter ofoxalic acid, as well as a very smaltquantily of sodium salts. This liquor is now allowed to cool, which-may be hastened by artificial means, whereupon a considerable portion of the oxalic acid crystallizes out and is precipitated, and may be separated from the mother liquor, as by decanting the latter. If desired, the oxalic acid crystals may be further purified, as by re-crystallization from water (preferably containing hydrochloric acid). 'This mot-her liquor, still containing a considerable amount of oxalic so acid, is now available to receive a fresh supply of sodium oxalate (preferably with further hydrochloric. acid gas), or a fresh quantity of hydrochloric acid gas alone, for repeating the operation and recovering a further yield of oxalic acid in solid .form. Briefly, I take sodium oxalate and an aque ous solution of hydrochloric acid, and ob tain separate yields of sodiumchlorid and. oxalic acid respectively, with the remaining,- mother liquor ready for repeating the process. The resultant sodium chlorid may be converted, by well-known electrolytic and chemical methods, into caustic soda and hydrchloric acid in equivalent quantities-the 5 former available for the preparation of further sodium oxalate as raw material, and the latter for decomposing said sodium oxalate, to produce fresh yields of sodium chlorid and oxalic acid; and so on, ad infinitmru'as a cyclic commercial process.

While the foregoing is a preferred formula, yet it may be varied considerably as to proportions, temperature, and treatment, without departing from the spirit of my inrentiou. For instance, for a given quantity of sodium oxalate, a larger or smaller quantity of the hydrochloric solution may be employed than that indicated (four .to one), and the strength of the solution (whether of greater or of less volume) may vary considerably below complete saturation with the gas; but, in general, the stronger the solution, (especially if its strength be maintained to the close of the treatment) and the greater its relative amount, the better the result; and where the introduction of hydrochloric acid in the form of gas is directed, it may be applied in the form of an already-prepared aqueous solution or in both forms. The temperature also may vary within a wide range, since the purpose of using elevated temperature is to be ab to lower it and'thereby precipitate oxai-n acid; for instance, if the treatment shouh be carried out at normal temperature, fl! precipitation could be effected by artificially cooling the mother liquor below normal; although, as already stated, oxalic acid can be otherwise recovered by well -known means. lot, I prefer the formula above set forth-substantially four parts of solution kept completely saturated (or nearly satu rated) with the gas, to one part of the-oxeration.

alate, and a temperature of around 70 centlgrade.

Although I have described the preferred form of my process as comprising as the the first step the hydrochloric-acid treatment, followed by the removal, of the dium chlorid and thereafter by the recovery of solid oxallc acid from the mother liquor, yet my invention is not limited to this order of steps, inasmuch as hydrochloric acid may befurther applied atlater stages of the op- For instance, after the original treatment with hydrochloric acidand after the removal of the sodium chlorid from the solution, as :lbove setforth', but before reacid.

covery of any oxalic acid, further hydrochloric acid gas may be run into the (un-. cooled) mother liquor (with or without fresh quantities Of'SGClItIm oxalate), and the resultant sodium chlorid removed and further oxalic acid the1i recovered, as before; and this may be repeated upon the same mother liquor as often as found desirable; or the mother liquor may first be cooled and some oxalic acid thereby recovered, and thereafter the gas run im followed by removal of the chlorid and recovery of.

furtheroxalic acid. In short, the saturation of the mother liquor (with the gas) need not be during the first stage (the original hydrochloric reaction), but may be effected at later stages of'theoperation.

I have referred broadly to sodium salts of oxalic acid, but for commercial reasons I prefer sodium oxalate, (Na C OQ as the body to .be treated with hydrochloric However, sodium hydrogen oxalate (-NaHC O,) may be substituted, without change of quantities, conditions, etc; so that where I speak of sodium oxalate, sodium hydrogen oxalate also is included. And, in general, any salt of oxalic acid may be employed that, when treated with an ex-' fresh supply of hydrochloric-aci 'l in said mother-liquor, and recovering further yields ofoxalic-acid therefrom is" above.

2, The process of, manufacturing oxalicacid, which'consists in treating sodium-oxalate with hydrochloric-acid in the presence of water to-producosolid sodium-chlorid.

and oxalic-acid in solution, then separating said chlorid 'fromfthe solution, recovering oxalic-acid from the mother-liquor,andtheit adding fresh quantities of sodium-oxalate and lrvdrochlOric-abid to said n'iother-liqum' to producea further yield of oxalic-acid.

3. The process of producing oxalic acid, which consists in first producing sodiumchlorid in solid form and oxalic-acid in solution by treatment of sodlum-oxalate with an excess of concentrated hydrochloric-acid solution, then separating the solid chlorid from the mother-liquor, and recovering: o x

alicac'id from the latter. in any suitable manner.

' l. The process of producing oxalic-acid, which consists in first producing sodium chlorid in solid form and oxalic-acid in so lution by treating sodium-oxalate with aii excess of concentrated hydrochloric-acid -s0- lution at an elevated temperature, then separating the solid chlorid from the' motherliquor, and recovering oxalic-acid from the latter by reduction of temperature.

The process of inanufacturiilg oxalicacid, which consists in treating sodium-oxalate with an excess of hydrochloric-acid.so-

lution at a temperature of about centi'-' grade, then drawing oil the hot mother liquor containing oxalic-acid in'. solution, and then lowering the temperature of sa d mother-liquor and thereby precipitating oxalic-aci'd, and finally drawing oifthe motherliquor to leave the solid pxalic acid.

G. The process ofprodncin oxalic -acid by treating sodium-oxalate wi h hydroch'J- rie-acid in the presence of warer and; at an elevated temperature, thenv removing the resultant solid sodium-chlorid from the mother-liquor, and finally recovering oxalicacid from the mother-liquor by cooling the latter.

7. Theproeess of producing oxalic-acid, which consists in treating sodium-oxalate with hydrochloric-acid to produce sodiumchlorid' in solid form and oxalic-acid in solution, then separating the solution from the solid sodium-chlorid, and finally recovering oxalic-acid from the solution inany suitable manner. r

8. In-the process or producing oxalicacid, the step which consists in treati 1g sodiumoxalate with an excess of conce trated hydrochloricacid solution.

9. In the process of producing oxalic-acid the step which consists in treating; sodiumoxalate with concentrated hydroch orie-aeid solution.

l0.'In the process of making oxalic-acid which consists in reacting on said salt wit 1 concentrated hydrochloric-acid in presence of water, and then separating the products formed.

11. In the process of making oxalic-acid from a sodium-salt of the same, the steps which consist in reacting on said salt with concentrated hydrochloric acid solution while in heated condition, and then lowering the temperature to recover one of the resulting products.

12. The process of making oxalic-acid from a sodium-saltof the same, consisting in applying to said salt an aqueous hydrochloric-acid solution, passing hydrochloric acid-gas into said solution, removing the solid product-,- and lowering the temperature to precipitate oxalic-acid.

13. .The process of producing oxalic-acid,

by treating a sodium-salt thereof witlrhydroehlorie-acid in such manner as to produce an insoluble chlorid and oxalic-acid in solution, and then recovering the oxalic-acid.

14. In the process of producing oxalicacid the step which consists in treating a sodium-salt thereof with concentrated hydrochloric-acid.

15. The process of making oxalic-acid from a salt of the same, consisting in reacting on said salt with an aqueous solution of hydrochloric-acid and thereby producing the chlorid in solid form and oxalic-acid in solution, and then recovering oxalic-acid from the mother-liquor.

In testimony whereof I have signed this specification in the presence of two subscril) ing witnesses.

v FRANK AUSTIN LIDBURY.

"itnesseS:

HELEN \Vnurnsn- Bsnrono, I'IAZEL Ina SHEAF. 

